Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants that are a human health concern because they are implicated in human cancers and endocrine disruption. The fish Fundulus heteroclitus will be used as a model organism to investigate the central hypothesis that CYP1B and/or CYP19 are involved in the molecular mechanisms of benzo(a)pyrene-mediated toxicity. The Specific Aims are to: 1) Assess the respective roles of CYP1B and CYP19s in BaP and estrogen metabolism and estrogen synthesis with in vitro recombinant systems, 2) Determine the extent, to which BaP-induced CYP1 B-mediated metabolism is important in genotoxicity. Aim 2.1: In adult fish following BaP exposure, the relationship between tissue specific CYP1B expression, toxic metabolite formation, DNA adducts and oxidative stress will be quantitated. Aim 2.2: Determine how egg or larval BaP-exposure affects CYP1B expression and associated toxicological endpoints. Aim 2.3: Determine how CYP1B and CYP19 are up-regulated in tumor tissues in exposed fish. 3) Measure the association between BaP-induced changes in aromatase and Fundulus reproductive or developmental success. Aim 3.1: Determine if maternal BaP-exposure decreases reproductive success. Aim 3.2: Determine if and how egg and larval BaP exposures alter aromatase expression and if this is correlated with developmental deficiencies. Successful completion of these Aims will provide a greater molecular understanding of these important P450 genes and their role in the mechanisms of action of PAHs. This research will further define the utility of Fundulus as a model organism for studying PAH-associated toxicities and in the development of human CYP19 or CYP1 B-related therapeutics.